We were on the 9 May Emerald sailing and when we checked in we received a letter detailing these requirements. Obviously they have been relaxed in the two sailings since then.
My observations were that for our sailing mask compliance as the per requests was good. Certainly very good compliance on the tenders and in the theatre. Still didn't stop Covid cases on the ship though.
Now that the US has caught up with most of the world and not requiring testing to return, it must soon be time to just be like the UK and have no requirements/restrictions. We just spent 10 days there after our Emerald cruise and it was great not to ever have to worry about masks. Of course, if people have personal health reasons to keep wearing masks then do so. If you are worried about Covid on cruises, then don't cruise. JMO.